The invention relates generally to the field of devices for erasing data on hard drive disk media. More particularly, the invention relates to structures for such devices that have magnetic fields structured to optimize the erasing capability of the device while minimizing possibility of damage to the disk drive and spindle motors.
To reuse defective hard drives in the process of manufacturing magnetic hard drives, a disk erase process is often used. A conventional disk erase process is DC erase with a servo track writer. While the foregoing procedure can achieve complete erase, it is time consuming and not suitable for mass production. Another method known in the art is to use an external magnetic field source such as a permanent magnet dipole and apply the magnetic field directly onto the hard drive. This method can be very fast as it can be done with hard drive intact. There are a few difficulties with this method that must be addressed. The first difficulty is the required magnetic field magnitude. With the advance of magnetic recording media technology, the coercivity of the magnetic media in a disk drive is much more than in earlier media. High coercivity media requires ever higher magnetic field amplitude for erasing. The second difficulty is the eddy current generated in the disks themselves, which have an aluminum substrate. The higher the magnetic field amplitude, the stronger the eddy current. It is necessary that the disks will be able to overcome the eddy current and achieve at least one rotation under the externally applied magnetic field. The third difficulty is that with ever higher magnetic erasing field amplitudes, the spindle motor will be exposed to the higher amplitude magnetic field. It must be ensured that the spindle motor will function properly after the erase procedure is completed.